1. Field of the Invention
The present invention relates to surface-treating agents, surface-treated powders, and cosmetics comprising the same, and in particular, relates to the improvement of hydrophobicity and rinsability of the powder used in cosmetics.
2. Prior Art
For cosmetics, especially for makeup cosmetics, the beautifying effect, which makes people beautiful, is naturally expected. In addition, the sustainability of the beautifying effect, namely, long-lasting makeup is one of very important required characteristics. Thus, in the development of cosmetic base material, one of important themes has been longer-lasting makeup. In the field of makeup cosmetics, oily bases are often used so that the makeup does not deteriorate with moisture such as sweat, tears, and saliva. When hydrophilic powder is blended in an oily base, the powder easily separates from the base. In addition, the hydrophilic powder is washed away with moisture, and it becomes a major cause of makeup deterioration. In the past, when powder was blended into cosmetics, the powder that had been hydrophobized in advance was often used for blending.
There are numerous methods for the hydrophobization of powder used in cosmetics. For example, a powder hydrophobization method, in which higher fatty acids, higher alcohols, hydrocarbons, triglycerides, esters, silicones such as silicone oil and silicone resin, or fluorine compounds are used, has been practiced to cover the surface of hydrophilic powder. In particular, the powder hydrophobizing treatment, in which silicones are used as the surface-treating agent, can provide excellent hydrophobicity. Thus, numerous methods have been established so far (refer to patent literatures 1 and 2, for example). In recent years, a method in which a copolymer of acrylic acid and acrylic acid ester is used as the powder surface-treating agent is also known (refer to patent literature 3, for example).
On the other hand, the rinsability of cosmetics is also one of the important required characteristics. When the above-described conventional hydrophobized powder is blended, a longer-lasting makeup can be achieved. However, the makeup cannot be easily rinsed away with water, even when soap is used, because of the excellent hydrophobicity. Therefore, oily cleansing agents have been widely used, however, it also becomes necessary to wash away this oily cleansing agent with soap. Thus, the burden to users becomes high. When hydrophilic powder is blended to allow easy rinsing, the makeup easily deteriorates and the makeup is short-lasting as described above. Thus, it has been a very difficult theme to satisfy both the characteristics: long lasting makeup in use and easy rinsing after use.    Patent literature 1: Japanese Unexamined Patent Publication S60-163973    Patent literature 2: Japanese Unexamined Patent Publication S62-177070    Patent literature 3: Japanese Unexamined Patent Publication H8-337514